Difluorophenyl pyrimidyl pyridine derivatives and the use thereof in liquid crystal mixtures

ABSTRACT

Difluorophenylpyrimidylpyridine derivatives of the formula (I) ##STR1## wherein X is N and Y is CH or X is CH and Y is N; 
     R 1  and R 2  are identical or different and are 
     a) an unbranched or branched alkyl chain having 1 to 20 carbon atoms, where 
     aa) one or more non-adjacent and non-terminal CH 2  groups may be replaced by --O--, --CO--O--, --O--CO--, --O--CO--O-- or --Si(CH 3 ) 2  --, and/or 
     ab) one or more H atoms may be replaced by F, and/or 
     ac) the terminal CH 3  group may be replaced by one of the following chiral groups (optically active or racemic): ##STR2## R 3 , R 4  and R 5  are identical or different and are hydrogen or a straight-chain or branched alkyl radical having 1-16 carbon atoms (with or without an asymmetrical carbon atom), where, in addition, one or more non-adjacent non-terminal CH 2  groups may be replaced by --O--, and/or where one or more H atoms of the alkyl radical may be substituted by --F; R 4  and R 5  may alternatively together be --(CH 2 ) 4  -- or --(CH 2 ) 5  -- if they are bonded to a dioxolane system, 
     are suitable as components, in particular, of ferroelectric liquid-crystal mixtures.

This application is a 371 of PCT/EP96/05774 filed Dec. 20, 1996.

In addition to nematic and cholesteric liquid crystals, optically activetilted smectic (ferroelectric) liquid crystals have also been usedrecently in commercial display devices.

Clark and Lagerwall have been able to show that the use of ferroelectricliquid crystals (FLCs) in very thin cells results in optoelectricalswitching or display elements which have response times faster by afactor of up to 1000 compared with conventional TN ("twisted nematic")cells (see, for example, EP-A 0 032 362). On the basis of this and otherfavorable properties, for example the possibility of bistable switchingand the virtually viewing angle-independent contrast, FLCs arefundamentally highly suitable for areas of application such as computerdisplays.

For the use of FLCs in electro-optical or fully optical components,either compounds are required which form tilted or orthogonal smecticphases and are themselves optically active, or ferroelectric smecticphases can be induced by doping compounds which, although forming suchsmectic phases, are not themselves optically active, with opticallyactive compounds. The desired phase should be stable over the broadestpossible temperature range.

In order to achieve good contrast in electro-optical components, auniform planar alignment of the liquid crystals is necessary. Goodalignment in the S_(A) and S*_(C) phase can be achieved, for example, ifthe phase sequence of the liquid-crystal mixture is, with decreasingtemperature:

    isotropic-N*-S.sub.A -S*.sub.C

The prerequisite is that the pitch of the helix in the N* phase is verylarge (greater than 10 μm) or, even better, is fully compensated (see,for example, T. Matsumoto et al., pp. 468-470, Proc. of the 6th Int.Display Research Conf., Japan Display, Sep. 30-Oct. 2, 1986, Tokyo,Japan; M. Murakami et al., ibid. pp. 344-347). This is achieved byadding one or more optically active dopes which induce a right-handhelix to the chiral liquid-crystal mixture which has, for example, aleft-hand helix in the N* phase, in such amounts that the helix iscompensated.

A further prerequisite for the use of the SSFLCD effect(surface-stabilized ferroelectric liquid-crystal display) of Clark andLagerwall for uniform planar alignment is that the pitch in the smecticC* phase is significantly greater than the thickness of the displayelement (Mol. Cryst. Liq. Cryst. 94 (1983), 213 and 114 (1984), 151). Asin the case of the cholesteric pitch, this is achieved by using dopeshaving the opposite rotation of the helix.

The optical response time τ[μs] of ferroelectric liquid-crystal systems,which should be as short as possible, depends on the rotationalviscosity of the system γ[mPas], the spontaneous polarization P_(s)[nC/cm² ] and the electric field strength E[V/m], in accordance with theequation ##EQU1##

Since the field strength E is determined by the electrode separation inthe electro-optical component and by the applied voltage, theferroelectric display medium must have low viscosity and a highspontaneous polarization to achieve a short response time.

Finally, in addition to thermal, chemical and photochemical stability, asmall optical anisotropy Δn and a low positive or preferably negativedielectric anisotropy Δε are required (see, for example, S. T. Lagerwallet al., "Ferroelectric Liquid Crystals for Displays", SID Symposium,Oct. Meeting 1985, San Diego, Calif., USA).

The totality of these requirements can only be achieved by means ofmixtures comprising a plurality of components. The base (or matrix) usedpreferably comprises compounds which if possible themselves already havethe desired phase sequence I-N-S_(A) -S_(C). Further components of themixture are frequently added in order to reduce the melting point and tobroaden the S_(C) and usually also the N phase, to induce opticalactivity, for pitch compensation and to match the optical and dielectricanisotropy; however, the rotational viscosity, for example, should ifpossible not be increased.

Ferroelectric liquid-crystal displays can also be operated by utilizingthe DHF (distorted helix formation) effect or the PSFLCD effect(pitch-stabilized ferroelectric liquid-crystal display, also known asSBF=short pitch bistable ferroelectric effect). The DHF effect has beendescribed by B. I. Ostrovski in Advances in Liquid Crystal Research andApplications, Oxford/Budapest, 1980, 469 ff.; the PSFLCD effect isdescribed in DE-A 39 20 625 and EP-A 0 406 346. In contrast to theSSFLCD effect, utilization of these effects requires aliquid-crystalline material having a short S_(C) pitch.

Derivatives of 1,2-difluorobenzene are disclosed as liquid crystals oras components of liquid-crystalline mixtures in, for example, DE-A 38 07871 and DE-A 38 07 862. Pyridylpyrimidines are disclosed, for example,in WO-A 92/12974 and U.S. Pat. No. 4,668,425.

However, since the development of ferroelectric liquid-crystal mixturesin particular can in no way be regarded as complete, the manufacturersof displays are interested in a very wide variety of components formixtures. Another reason for this is that only the interaction of theliquid-crystalline mixtures with the individual components of thedisplay device or of the cells (for example the alignment layer) allowsconclusions to be drawn on the quality of the liquid-crystallinemixtures too.

The object of the present invention was therefore to provide compoundswhich are suitable in liquid-crystalline mixtures for improving theproperty profile of these mixtures.

It has now been found, surprisingly, thatdifluorophenylpyrimidylpyridine derivatives of the formula (I) areparticularly suitable for use in liquid-crystal mixtures.

The invention therefore relates to compounds of the formula (I) ##STR3##in which the symbols are defined as follows: X is N and Y is CH or X isCH and Y is N;

R¹ and R² are identical or different and are

a) an unbranched or branched alkyl chain having 1 to 20 carbon atoms,where

aa) one or more non-adjacent and non-terminal CH₂ groups may be replacedby --O--, --CO--O--, --O--CO--, --O--CO--C-- or --Si(CH₃)₂ --, and/or

ab) one or more H atoms may be replaced by F, and/or

ac) the terminal CH₃ group may be replaced by one of the followingchiral groups (optically active or racemic): ##STR4## b) hydrogen, whereonly one of the two radicals R¹ and R² can be H,

with the proviso that R¹ must not be bonded to the pyridine ring via--CO--O-- or --O--CO--O--;

R³, R⁴ and R⁵ are identical or different and are hydrogen or astraight-chain or branched alkyl radical having 1-16 carbon atoms (withor without an asymmetrical carbon atom), where, in addition, one or morenon-adjacent, non-terminal CH₂ groups may be replaced by --O--, and/orwhere one or more H atoms of the alkyl radical may be substituted by--F; R⁴ and R⁶ may alternatively together be --(CH₂)₄ -- or --(CH₂)₅ --if they are bonded to a dioxolane system.

Preference is given to compounds of the formula (I) in which the symbolshave the following meanings:

R¹ and R² are identical or different and are

a) an unbranched or branched alkyl chain having 1 to 16 carbon atoms,where

aa) one or more non-adjacent and non-terminal CH₂ groups may be replacedby --O--, --CO--O--, O--CO--, --O--CO--O-- or --Sl(CH₃)₂ --, and/or

ab) one or more H atoms may be replaced by F, and/or

ac) the terminal CH₃ group may be replaced by one of the followingchiral groups (optically active or racemic): ##STR5## b) hydrogen, whereonly one of the two radicals R¹ and R² can be H,

with the proviso that R¹ must not be bonded to the pyridine ring via--CO--O-- or --O--CO--O--;

R³, R⁴ and R⁵ are identical or different and are hydrogen or astraight-chain or branched alkyl radical having 1-13 carbon atoms,where, in addition, one or more non-adjacent, non-terminal CH₂ groupsmay be replaced by --O--, and/or where one or more H atoms of the alkylradical may be substituted by --F; R⁴ and R⁵ may alternatively togetherbe --(CH₂)₄ -- or --(CH₂)₅ -- if they are bonded to a dioxolane system.

Particular preference is given to compounds of the formula (I) in whichthe symbols have the following meanings:

R¹ and R² are identical or different and are

a) an unbranched or branched alkyl chain having 1 to 12 carbon atoms,where

aa) one or more non-adjacent and non-terminal CH₂ groups may be replacedby --O--, --CO--O--, --O--CO-- or --O--CO--O--, and/or

ab) one or more H atoms may be replaced by F, and/or

ac) the terminal CH₃ group may be replaced by one of the followingchiral groups (optically active or racemic): ##STR6## b) hydrogen, whereonly one of the two radicals R¹ and R² can be H,

with the proviso that R¹ must not be bonded to the pyridine ring via--CO--O-- or --O--CO--O--;

R³ is identical or different and is hydrogen or a straight-chain orbranched alkyl radical having 1 to 10 carbon atoms where, in addition,one or two non-adjacent, non-terminal CH₂ groups may be replaced by--O--.

Very particular preference is given to compounds of the formula (I) inwhich the symbols have the following meanings:

R¹ and R² are identical or different and are

a) an unbranched or branched alkyl chain having 1 to 12 carbon atoms,where

aa) one or more non-adjacent and non-terminal CH₂ groups may be replacedby --O--, --CO--O--, --O--CO--, or --O--CO--O--, and/or

ab) the terminal CH₃ group may be replaced by one of the followingchiral groups (optically active or racemic): ##STR7## b) hydrogen, whereonly one of the two radicals R¹ and R² can be H,

with the proviso that R¹ must not be bonded to the pyridine ring via--CO--O-- or --O--CO--O--;

R³ is identical or different and is hydrogen or a straight-chain orbranched alkyl radical having 1 to 10 carbon atoms, where, in addition,one or more non-adjacent, non-terminal CH₂ groups may be replaced by--O--.

The compounds according to the invention are prepared by methods knownper se from the literature, as described in the standard works oforganic synthesis, for example Houben-Weyl, Methoden der OrganischenChemie, [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart.

The preparation is carried out under reaction conditions which are knownand suitable for said reactions. Use can also be made here of variantswhich are known per se, but are not mentioned here in greater detail.

If desired, the starting materials an also be formed in situ by notisolating them from the reaction mixture, but instead immediatelyconverting them into the compounds of the formula (I).

Schemes 1 and 2 show by way of example synthetic routes to compounds ofthe formula (I), although other processes are feasible and possible.

The compounds of the formula (I) according to the invention can beprepared, for example, by the following synthetic schemes by combiningthe building blocks mentioned therein with the aid of transitionmetal-catalyzed cross-coupling reactions (for example as described inEP-A 0 679 619, EP-A 0 694 530 and DE-A 42 36 103): ##STR8##

The starting compounds are either known or can be prepared analogouslyto known compounds.

For example, 2,3-difluorophenylboronic acid and4-alkoxy-2,3-difluorophenylboronic acids are described in WO 96/00710;4-benzyloxy-2,3-difluorophenylboronic acid can also be obtainedanalogously (WO 96/01246). Examples of 4-alkyl-substituted2,3-difluorophenylboronic acids are given in EP-A 0 363 458.

5-Bromo-2-chloropyrimidine can be obtained in two steps starting fromcommercial 2-hydroxypyrimidine hydrochloride by reaction with bromine inaqueous solution (cf. D. G. Crosby, R. V. Berthold, J. Org. Chem. 1960,25, 1916-1919) followed by chlorination using POCl₃ /triethylamine (cf.(D. J. Brown, J. M. Lyall, Australian J. Chem. 1964, 17, 794-802).

The synthesis of 2,5-dibromopyrimidine is described by way of example inU.S. Pat. No. 5,371,224.

2-Alkoxypyridine-5-boronic acids can be prepared starting fromcommercial 2,5-dibromopyridine in accordance with the following scheme:##STR9##

Ethers of the formula (I) are also obtainable by etherification of thecorresponding phenols (R² =OH), where the phenol is advantageously firstconverted into a corresponding metal derivative, for example into thecorresponding alkali metal phenoxide by treatment with NaH, NaNH₂, NaOH,KOH, Na₂ CO₃ or K₂ CO₃. This phenoxide can then be reacted with thecorresponding alkyl halide, alkyl sulfonate or dialkyl sulfate,advantageously in an inert solvent, such as acetone,1,2-dimethoxyethane, DMF (dimethylformamide) or dimethyl sulfoxide, oralternatively with an excess of aqueous or aqueous-alcoholic NaOH or KOHat temperatures between about 20° C. and 100° C.

The etherification can also be carried out, for example, by reactingphenols of the formula (I) with alcohols using diethyl azodicarboxylateand triphenylphosphine by the so-called Mitsunobu method (cf. O.Mitsunobu, Synthesis 1981, 1-28, or L. Navallies, H. T. Nguyen, P.Barois, Liq. Cryst. 1996, 20, 653-664).

The corresponding alcohols, alkyl halides, alkyl sulfonates and dialkysulfates are either known or can be prepared analogously to knownprocesses.

Phenols of the formula (I) (R² =OH) can also be prepared by removing asuitable protecting group, for example from the corresponding benzyloxycompound by hydrogenation on the Pd/C, or from the correspondingunsubstituted compound (R² =H) by a process analogous to WO 96/00710 orC. C. Dong, M. Hird, J. W. Goodby, P. Styring, K. J. Toyne,Ferroelectrics 1996, 180, 245-257.

Esters of the formula (I) can also be obtained by esterification of thecorresponding carboxylic acids (or reactive derivatives thereof) usingphenols of the formula (I) (R² =OH) or reactive derivatives thereof. Anexample of a suitable process for this purpose is the so-called DCCmethod (DCC=dicyclohexylcarbodiimide; cf. B. Neises, W. Steglich, Angew.Chem. 1978, 90, 556-557). Esters of the formula (I) can also be obtainedfrom the corresponding carboxylic acid salts (preparation in accordancewith DE-C 4304756) by reaction with phenols as described in DE-A4427198.

The corresponding carboxylic acids are either known or can be preparedby known processes.

Particularly suitable reactive derivatives of said carboxylic acids arethe acid halides, especially the chlorides and bromides, furthermore theanhydrides, for example also mixed anhydrides, azides or esters, inparticular alkyl esters having 1-4 carbon atoms in the alkyl group.

Particularly suitable reactive derivatives of said phenols are thecorresponding metal phenoxides, preferably of an alkali metal, such assodium or potassium.

The esterification is advantageously carried out in the presence of aninert solvent. Particularly suitable solvents are ethers, such asdiethyl ether, dibutyl ether, THF, dioxane or anisole, ketones, such asacetone, butanone or cyclohexanone, amides, such as DMF orhexamethylphosphoric triamide, hydrocarbons, such as benzene, toluene orxylene, halogenated hydrocarbons, such as tetrachloromethane,dichloromethane or tetrachloroethylene, and sulfoxides, such as dimethylsulfoxide or sulfolane.

A carboxylate group is introduced into compounds of the formula (I) by,for example, a process analogous to GB-A 1098387 or A. M. Roe, R. A.Burton, D. R. Reavill, J. Chem. Soc., Chem. Commun. 1965, 22, 582, bylithlation of the corresponding unsubstituted compounds of the formula(I) (R² =H) using n-butyllithium and reaction with carbon dioxide.Subsequent esterification of the resulting carboxylic acids of theformula (I) (R² =COOH) or reactive derivatives thereof usingcorresponding hydroxyl compounds (or reactive derivatives thereof) canbe carried out analogously to the procedure described above.

Said hydroxyl compounds (or reactive derivatives thereof) are eitherknown or can be prepared analogously to known processes.

The introduction of alkyl substituents is also possible by reaction ofperfluoroalkylsulfonic esters of the formula (I) (R² =--O--SO₂ --C_(n)F_(2n+1)) with alkylboranes or with terminal alkynes (Heck reaction)with palladium catalysis (cf. EP-A 0 709 357). In the latter case, thereaction is followed by an additional catalytic hydrogenation. Suitablealkylboranes can be obtained by known methods, for example by reactionof terminal alkenes with 9-BBN; the said perfluoroalkylsulfonic esterscan be obtained from the respective phenols (R² =OH) by esterificationusing the corresponding sulfonic anhydrides.

Regarding the synthesis of specific radicals R¹ and R², we additionallyrefer to the following, for example:

EP-B 0 355 008 for compounds having silicon-containing side chains,

EP-B 0 292 954 for optically active compounds containing an oxiraneester unit,

EP-B 0 263 437 for optically active compounds containing an oxiraneether unit,

EP-B 0 361 272 for optically active compounds containing a dioxolaneester unit,

EP-B 0 351 746 for optically active compounds containing a dioxolaneether unit,

U.S. Pat. No. 5,051,506 for optically active compounds containing a2,3-difluoroalkoxy unit,

U.S. Pat. No. 4,798,680 for optically active compounds containing a2-fluoroalkoxy unit,

U.S. Pat. No. 4,855,429 for optically active compounds containing anα-chlorocarboxylic acid unit.

The provision of compounds of the formula (I) very generallyconsiderably broadens the range of liquid-crystalline substances whichare suitable, from various applicational points of view, for thepreparation of liquid-crystalline mixtures.

In this connection, the compounds of the formula (I) have a broad rangeof applications. Depending on the choice of substituents, they can beused as base materials of which liquid-crystalline phases arepredominantly composed; however, it is also possible to add compounds ofthe formula (I) to liquid-crystalline base materials from other classesof compound in order, for example, to modify the dielectric and/oroptical anisotropy of a dielectric of this type and/or to optimize itsthreshold voltage and/or its viscosity.

The invention also relates to the use of compounds of the formula (I) inliquid-crystal mixtures, preferably ferroelectric liquid-crystalmixtures, in particular ferroelectric liquid-crystal mixtures employedin display devices which are based on utilization of the SSFLCD (surfacestabilized ferroelectric liquid crystal display) effort, in particularthe so-called inverse or τV.sub.(min) mode.

The invention furthermore relates to liquid-crystal mixtures, preferablyferroelectric liquid-crystal mixtures, in particular ferroelectricliquid-crystal mixtures operated utilizing the SSFLCD effect and inparticular in so-called inverse or τV.sub.(min) mode, which comprise oneor more compounds of the formula (I).

The liquid-crystal mixtures according to the invention generallycomprise from 2 to 35, preferably from 2 to 25, particularly preferablyfrom 2 to 20 components.

They generally comprise from 0.01 to 80% by weight, preferably from 0.1to 60% by weight, particularly preferably from 0.1 to 30% by weight, ofone or more, preferably 1 to 10, particularly preferably 1 to 5, veryparticularly preferably 1 to 3, of the compounds of the formula (I)according to the invention.

Further components of liquid-crystal mixtures comprising compounds ofthe formula (I) according to the invention are preferably selected fromknown compounds having smectic and/or nematic and/or cholesterol phases.These include, for example:

derivatives of phenylpyrimidine, as described, for example, in WO86/06401 and U.S. Pat. No. 4,874,542,

meta-substituted aromatic compounds having a six-membered ring, asdescribed, for example, in EP-A 0 578 054,

silicon compounds, as described, for example, in EP-B 0 355 008,mesogenic compounds containing only one side chain, as described, forexample, in EP-A 0 541 081,

hydroquinone derivatives, as described, for example, in EP-A0 603 786,

phenylbenzoates, as described, for example, in P. Keller, Ferroelectrics58 (1984), 3, and J. W. Goodby et al., Liquid Crystals and OrderedFluids, Vol. 4, New York, 1984, and

thiadiazoles as described, for example, in EP-B 0 309 614.

Examples of suitable chiral, non-racemic dopants are:

optically active phenylbenzoates, as described, for example, in P.Keller, Ferroelectrics 58 (1984), 3, and J. W. Goodby et al., LiquidCrystals and Ordered Fluids, Vol. 4, New York, 1984,

optically active oxirane ethers, as described, for example, in EP-B 0263 437 and WO-A 93/13093,

optically active oxirane esters, as described, for example, in EP-B 0292 954,

optically active dioxolane ethers, as described, for example, in EP-B 0351 746,

optically active dioxolane esters, as described, for example, in EP-B 0361 272,

optically active tetrahydrofuran-2-carboxylic esters, as described, forexample, in EP-B 0 355 561, and

optically active 2-fluoroalkyl ethers, as described, for example, inEP-B 0 237 007 and U.S. Pat. No. 5,051,506.

Suitable further mixture components are listed, in particular, ininternational patent application PCT/EP 96/03154, which is expresslyincorporated herein by way of reference.

The mixtures can in turn be used in electro-optical or fully opticalelements, for example display elements, switching elements, lightmodulators, elements for image processing and/or signal processing orgenerally in the area of nonlinear optics.

The mixtures are furthermore suitable for field treatment, i.e. foroperation in the quasi-bookshelf geometry (QBG) (see, for example, H.Rieger et al., SID 91 Digest (Anaheim), 1991, p. 396).

The ferroelectric liquid-crystal mixtures according to the invention areparticularly suitable for operation in so-called inverse or τV.sub.(min)mode (see, for example, J. C. Jones, M. J. Towler, J. R. Huges, Displays14 (1993), No. 2, 86-93: M. Koden, Ferroelectrics 179 (1996), 121-129).

When operated in inverse mode, FLC mixtures according to the inventionare distinguished by advantageous figures of merit, as defined in A. J.Slaney, V. Minter, J. C. Jones, Ferroelectrics 178 (1996), 65-74. Theyare therefore particularly useful for practical use in switching and/ordisplay devices (displays).

Liquid-crystalline mixtures comprising compounds of the formula (I) areparticularly suitable for use in electro-optical switching and displaydevices (displays). These displays are usually constructed in such a waythat a liquid-crystal layer is enclosed on both sides by layers whichare usually, in this sequence starting from the LC layer, at least onealignment layer, electrodes and a limiting sheet (for example of glass).In addition, they may contain spacers, adhesive frames, polarizers and,for color displays, thin color-filter layers. Other possible componentsare antireflection, passivation, compensation and barrier layers andelectric non-linear elements, such as thin-film transistors (TFTs) andmetal-insulator-metal (MIM) elements. The structure of liquid-crystaldisplays has already been described in detail in relevant monographs(see, for example, E. Kaneko, "Liquid Crystal TV Displays: Principlesand Applications of Liquid Crystal Displays", KTK Scientific Publishers,1987).

The invention therefore furthermore relates to a switching and/ordisplay device, in particular a ferroelectric switching and/or displaydevice, which contains a liquid-crystal mixture comprising one or morecompounds of the formula (I).

This switching and/or display device according to the invention ispreferably operated in normal or inverse mode.

Ferroelectric switching and/or display devices operated by multiplexaddressing can be operated, inter alia, in two different ways, normalmode or inverse mode (also known as τV.sub.(min) mode). The differencebetween the two is in the addressing scheme and in the variousrequirements of the dielectric tensor of the FLC material, i.e. the FLCmixture. A review is given, for example, by J. C. Jones et al. inDisplays 1993, 14, No. 2, 86-93, referred to below as "Jones" and M.Koden in Ferroelectrics 1996, 179, 121-129, and the references citedtherein.

The switching characteristics of a FLC device can generally berepresented by a diagram in which the driving voltage (V) is plotted onthe horizontal axis and the width of the addressing pulses (τ, time) isplotted on the vertical axis (see, for example, Jones, FIGS. 4, 8, 10and 11).

A switching curve is determined experimentally and divides the V, τ areainto a switching zone and a non-switching zone. When the voltage isincreased, the pulse width normally shortens, This behaviorcharacterizes normal mode (see, for example, Jones, FIG. 4).

In suitable materials, however, the Vτ curve exhibits a minimum (atvoltage V.sub.(min)), as evident, for example, in Jones in FIGS. 8, 10and 11. This minimum is caused by superimposed dielectric ferroelectrictwisting. FLC devices are operated in inverse mode if the sum of theline and column driving voltage in the working temperature region ishigher than the minimum on the Vτ curve, i.e. V.sub.(line) +V.sub.(line)>V.sub.(min).

The invention is explained in greater detail by the examples below,without being restricted thereto.

The following abbreviations are used:

abs. absolute

cl.p. clearing point

DCC N,N'-dicyclohexylcarbodiimide

DMAP 4-(dimethylamino)pyridine

DMF N,N-dimethylformamide

m.p. melting point

sat. saturated

THF tetrahydrofuran

v/v volume ratio

Furthermore, X=crystalline state, S=smectic phase (the index denotes thephase type), N=nemetic phase, I=isotropic phase. The numbers betweenthese symbols indicate the transition temperatures. Phase transitiontemperatures were determined by DTA, phase types by optical polarizationmicroscopy. All temperatures are given in degrees Celsius.

Precursor 1

Synthesis of 5-bromo-2-hexyloxypyridine

A solution of 300 mmol of 1-hexanol in 100 ml of DMF is added dropwiseat 50° C. under a protective gas to a suspension of 300 mmol of sodiumhydride (80 percent in mineral oil) in 100 ml of dry DMF. The mixture isstirred at 80° C. for 1 hour, and a solution of 200 mmol of2,5-dibromopyridine in 150 ml of warm DMF is subsequently slowly addeddropwise. The mixture is then stirred at 80° C. for 3-4 hours. Forhydrolysis, the cooled reaction mixture is introduced into 1 l ofice/water, the mixture is extracted a number of times withdichloromethane, and the combined organic extracts are washed with sat.sodium chloride solution and dried using sodium sulfate. After thesolvent has been removed in vacuo, the residue is chromatographed onsilica gel 60 using dichloromethane as eluent, giving 52 g (quant.yield) of a viscous liquid.

The following were prepared analogously:

5-bromo-2-butoxypyridine

5-bromo-2-octyloxypyridine

5-bromo-2-dodecyloxypyridine

Precursor 2

Synthesis of 2-hexyloxypyridine-5-boronic acid

250 mmol of n-butyllithium (1.6M solution in n-hexane) are addeddropwise at 0° C. with exclusion of moisture and under a protective-gasatmosphere to a solution of 250 mmol of 5bromo-2-hexyloxypyridine in 500ml of abs. diethyl ether. The mixture is stirred at this temperature fora further 1 hour, and 275 mmol of trimethyl borate are subsequentlyadded slowly. After the mixture has been stirred at 0° C. for a furtherhour, a solution of 175 ml of water and 25 ml of 37 percent hydrochloricacid is added dropwise. The mixture is stirred at room temperature for 1hour, the phases are then separated, the aqueous phase is extracted anumber of times with dichloromethane, and the combined organic extractsare dried using magnesium sulfate. The solvents are removed in vacuo.After drying in a high vacuum, the red-brown, high-viscosity crudeproduct is reacted further without additional purification.

The following were prepared analogously:

2-butoxypyridine-5-boronic acid

2-octyloxypyridine-5-boronic acid

2-dodecyloxypyridine-5-boronic acid

Precursor 3

Synthesis of 5-bromo-2-(6-hexyloxypyridin-3-yl)pyrimidine

233 mmol of 2-hexyloxypyridine-5-boronic acid, 300 ml of ethanol, asolution of 466 mmol of sodium carbonate in 150 ml of water and 2.3 mmolof tetrakis(triphenylphosphine)palladium(0) are added to a solution of233 mmol of 2,5-dibromopyrimidine in 600 ml of toluene. The mixture isheated at the boil until the reaction is complete. The organic phase isseparated off, the aqueous phase is extracted with dichloromethane, andthe combined organic extracts are dried using sodium sulfate. After thesolvent has been removed in vacuo, the crude product is separated off bycolumn chromatography on silica gel 60 using dichloromethane as eluentand is recrystallized from n-heptane, giving 31 g (40%) of a colorlesssolid. m.p. 103-106° C.

Precursor 4

Synthesis of 5-bromo-2-(6-butoxypyridin-3-yl)pyrimidine

A reaction of 109 mmol of 2,5-dibromopyrimidine, 109 mmol of2-butoxypyridine-5-boronic acid, 218 mmol of sodium carbonate and 1.1mmol of tetrakis(triphenylphosphine)palladium(0) in 200 ml of toluene,100 ml of ethanol and 100 ml of water is carried out analogously to theprocedure indicated for precursor 3. Corresponding purification gives12.4 g (37%) of a colorless solid, m.p. 134-138° C.

Precursor 5

Synthesis of 5-bromo-2-(6-octyloxypyridin-3-yl)pyrimidine

A reaction of 115 mmol of 2,5-dibromopyrimidine, 115 mmol of2-butoxypyrdine-5-boronic acid, 230 mmol of sodium carbonate and 1.2mmol of tetrakis(triphenylphosphine)palladium(0) in 280 ml of toluene,140 ml of ethanol and 140 ml of water is carried out analogously to theprocedure indicated for precursor 3. Corresponding purification gives15.9 g (38%) of a colorless solid, m.p. 99-101 ° C.

Precursor 6

Synthesis of 5-bromo2-(6-dodecyloxypyridin-3-yl)pyrimidine

A reaction of 35 mmol of 2,5-dibromopyrimidine, 27 mmol of2-dodecyloxypyridine-5-boronic acid, 64 mmol of sodium carbonate and 0.3mmol of tetrakis(triphenylphosphine)palladium(0) in 210 ml of toluene,135 ml of ethanol and 70 ml of water is carried out analogously to theprocedure indicated for precursor 3. Corresponding purification gives3.9 g (35%) of a colorless solid.

Precursor 7

Synthesis of 2-chloro-5-(6-hexyloxypyridin-3-yl)pyrimidine

A reaction of 5-bromo-2-chloropyrimidine and2-hexyloxypyridine-5-boronic acid is carried out analogously to theprocedure indicated for precursor 3. Corresponding purification gives acolorless solid.

Precursor 8

Synthesis of 5-(6-butoxypyridin-3-yl)-2-chloropyrimidine

A reaction of 109 mmol of 5-bromo-2-chloropyrimidine, 109 mmol of2-butoxypyridine-5-boronic acid, 218 mmol of sodium carbonate and 1.1mmol of tetrakis(triphenylphosphine)palladium(0) in 200 ml of toluene,100 ml of ethanol and 100 ml of water is carried out analogously to theprocedure indicated for precursor 3. Corresponding purification gives10.8 g (38%) of a colorless solid, m.p. 117° C., cl.p. 130° C.

Precursor 9

Synthesis of 2-chloro-5-(2,3-difluorophenyl)pyrimidine

A reaction of 288 mmol of 5-bromo-2-chloropyrimidine, 288 mmol of2,3-difluorophenylboronic acid, 576 mmol of sodium carbonate and 5.8mmol of tetrakis(triphenylphosphine)palladium(0) in 560 ml of toluene,280 ml of ethanol and 280 ml of water is carried out analogously to theprocedure indicated for precursor 3. Corresponding purification gives37.7 g (58%) of a colorless solid.

Precursor 10

Synthesis of 2-(4-benzyloxy-2,3-difluorophenyl)5-bromopyrimidine

A reaction of 14 mmol of 2,5-dibromopyrimidine, 17 mmol of4-benzyloxy-2,3-difluorophenylboronic acid, 34 mmol of sodium carbonateand 0.14 mmol of tetrakis(triphenylphosphine)palladium(0) in 100 ml oftoluene, 50 ml of ethanol and 50 ml of water is carried out analogouslyto the procedure indicated for precursor 3. Purification byrecrystallization from 2-propanol gives 1.4 g (26%) of a colorlesssolid, m.p. 138° C.

Precursor 11

Synthesis of5-(4-benzyloxy-2,3-difluorophenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidine

The reaction of 6 mmol of 5-bromo-2-(6-hexyloxypyridin-3-yl)pyrimidine,6 mmol of 4-benzyloxy-2,3-difluorophenylboronic acid, 12 mmol of sodiumcarbonate, 0.06 mmol of bis(dibenzylideneacetone)palladium(0) and 0.12mmol of triphenylphosphine in 50 ml of toluene, 25 ml of ethanol and 25ml of water is carried out analogously to the procedure indicated forExample 1a). Corresponding chromatographic purification gives 1.4 g(49%) of a colorless solid, m.p. 125° C., cl.p. 174° C.

Precursor 12

Synthesis of5-(4-benzyloxy-2,3-difluorophenyl-2-(6-dodecyloxypyridin-3-yl)pyrimidine

The reaction of 6 mmol of5-bromo-2-(6-dodecyloxypyridin-3-yl)pyrimidine, 6 mmol of4-benzyloxy-2,3-difluorophenylboronic acid, 12 mmol of sodium carbonate0.06 mmol of bis(dibenzylideneacetone)palladium(0) and 0.12 mmol oftriphenylphosphine in 50 ml of toluene, 25 ml of ethanol and 25 ml ofwater is carried out analogously to the procedure indicated for Example1a). Corresponding chromatographic purification gives 1.4 g (42%) of acolorless solid, m.p. 115° C., cl.p. 172° C.

Precursor 13

Synthesis of2-(4-benzyloxy-2,3-difluorophenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine

The reaction of 35 mmol of2-(4-benzyloxy-2,3-difluorophenyl)-5-bromopyrimidine, 44 mmol of2-octyloxypyridine-5-boronic acid, 70 mmol of sodium carbonate and 0.4mmol of tetakis(triphenylphosphine)palladium(0) in 120 ml of toluene, 60ml of ethanol and 60 ml of water is carried out analogously to theprocedure indicated for Example 1a). Corresponding chromatographicpurification and recrystallization from ethyl acetate gives 10.7 g (61%)of colorless crystals, m.p. 120° C., cl.p. 182-183° C.

Precursor 14

Synthesis of5-(2,3-difluoro-4-hydroxyphenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidine

1.5 g of 10 percent palladium/charcoal and 0.1 g of 4-toluenesulfonicacid are added to a solution of 14 mmol of5-(4-benzyloxy-2,3-difluorophenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidinein 200 ml of THF. The mixture is stirred at 50° C. under hydrogen in asuitable apparatus until the take-up of hydrogen is complete, thecatalyst is filtered off, and the solvent is removed in vacuo.Purification by recrystallization from acetonitrile gives 4.0 g (73%) ofa colorless solid, m.p. 150-155° C.

Precursor 15

Synthesis of5-(2,3-difluoro-4-hydroxyphenyl)-2-(6-dodecyloxypyridin-3-yl)pyrimidine

The hydrogenation of 2.5 mmol of5-(4-benzyloxy-2,3-difluorophenyl)-2-(6-dodecyloxypyridin-3-yl)pyrimidinein 50 ml of THF is carried out analogously to the procedure indicatedfor precursor 14, giving 0.7 g (60%) of a colorless solid, m.p. 111-118°C.

Precursor 16

Synthesis of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine

The hydrogenation of 21 mmol of2-(4-benzyloxy-2,3-difluorophenyl)-5-(6-octyloxypyridin-3-yl)pyrimidinein 200 ml of THF is carried out analogously to the procedure indicatedfor precursor 14, giving 8.2 g (93%) of a colorless solid, m.p. 130-132°C.

EXAMPLE 1 Synthesis of5-(2,3-difluoro-4-octyloxyphenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidine##STR10##

a) 58 mmol of 2,3-difluoro-4-octyloxyphenylboronic acid, 180 ml ofethanol, a solution of 116 mmol of sodium carbonate in 90 ml of waterand 0.6 mmol of tetrakis(triphenylphosphine)palladium(0) are added to asolution of 58 mmol of 5-bromo2-(6-hexyloxypyridin-3-yl)pyrimidine in360 ml of toluene. The mixture is heated at the boil until the reactionis complete. The organic phase is separated off, the aqueous phase isextracted with dichloromethane, and the combined organic extracts aredried using sodium sulfate. After the solvents have been removed invacuo, the crude product is separated off by column chromatography onsilica gel 60 using dichloromethene/ethyl acetate 20:1 (v/v) as eluentand is recrystallized from methanol, giving 11 g (63%) of colorlesscrystals, X 82.5 S_(C) 130 S_(A) 160 I.

b) The etherification of 12 mmol of5-(2,3-difluoro-4-hydroxyphenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidineusing 13.2 mmol of 1-bromooctane in 100 ml of DMF is carried outanalogously to the procedure indicated for Example 3. The crude productis chromatographed on silica gel 60 using dichloromethane as eluent andis recrystallized from n-heptane and toluene, giving 3.6 g (61%) ofcolorless crystals, whose analytical data correspond to those of thecompound obtained as described in 1a).

Example 2 Synthesis of5-(2,3-difluoro-4-octyloxyphenyl)-2-(6-dodecyloxypyridin-3-yl)pyrimidine##STR11##

The etherification of 1.3 mmol of5-(2,3-difluoro-4-hydroxyphenyl)-2-(6-dodecyloxypyridin-3-yl)pyrimidineusing 1.7 mmol of 1-bromooctane in 80 ml of DMF is carried outanalogously to the procedure indicated for Example 3. Chromatographicpurification on silica gel 60 using dichloromethane as eluent andrecrystallization from methanol gives 380 mg (51%) of colorlesscrystals, X 67 X₁ 76 S_(C) 118-123 S_(A) 147 I.

Example 3 Synthesis of2-(2,3-difluoro-4-octyloxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine##STR12##

A solution of 2.4 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine in10 ml of DMF is added dropwise at room temperature and under aprotective gas to a suspension of 2.7 mmol of sodium hydride (80 percentin mineral oil) in 5 ml of dry DMF. The mixture is stirred for a further30 minutes, and 2.7 mmol of 1-bromooctane, dissolved in 10 ml of DMF,are then added slowly. The reaction mixture is stirred at roomtemperature for 20 hours and introduced into 100 ml of ice/water, themixture is extracted a number of times with dichloromethane, and thecombined organic extracts are washed with sat. sodium chloride solutionand dried using magnesium sulfate. After the solvent has been removed invacuo, the crude product is chromatographed on silica gel 60 usingdichloromethane/ethyl acetate 20:1 (v/v) as eluent and recrystallizedfrom acetonitrile, giving 0.77 g (61%) of colorless crystals, X 89 S₃73.5 S_(C) 164 S_(A) 167 I.

Example 4 Synthesis of2-(2,3-difluoro-4-hexyloxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine##STR13##

The etherification of 2.4 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidineusing 2.7 mmol of 1-bromohexane is carried out analogously to theprocedure indicated in Example 3. Corresponding purification gives 0.88g (73%) of colorless crystals, X 81.5 S₃ 75.5 S_(C) 165.6 S_(A) 174 I.

Example 5 Synthesis of2-(4-butoxy-2,3-difluorophenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine##STR14##

The etherification of 2.4 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidineusing 2.7 mmol of 1-bromobutane is carried out analogously to theprocedure indicated for Example 3. Corresponding purification gives 0.76g (69%) of colorless crystals, X 85 S_(C) 156 S_(A) 180 I.

Example 6 Synthesis of2-(4-ethoxy-2,3-difluorophenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine##STR15##

The etherification of 2.8 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidineusing 3.0 mmol of 1-bromoethane is carried out analogously to theprocedure indicated for Example 3. Corresponding purification gives 0.62g (51%) of colorless crystals, X 111 S_(C) 122.5 S_(A) 185 I.

Example 7 Synthesis of2-[2,3-difluoro-4-(2-(S)-fluorodecyloxy)phenyl]-5-(6-octyloxypyridin-3-yl)pyrimidine##STR16##

3.2 mmol of diethyl azodicarboxylate are added dropwise at 0° C. to 3.2mmol of triphenylphosphine in 20 ml of THF, and the mixture is stirredat room temperature for a further 20 minutes. 2.4 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidineand 2.4 mmol of 2-(S)-fluorodecanol are then added, and the reactionmixture is allowed to stand overnight. After the solvent has beenremoved in vacuo, the crude product is chromatographed on silica gel 60using dichloromethane/ethyl acetate 20:1 (v/v) as eluent and isrecrystallized from acetonitrile, giving 1.2 g (86%) of colorlesscrystals, X 97 S_(C) * 150.5 S_(A) 161.5 I.

Example 8 Synthesis of2-[4-(3-butyl-(2S,3S)-oxiranylmethoxy)-2,3-difluorophenyl]-5-(6-octyloxypyridin-3-yl)pyrimidine##STR17##

The etherification of 2.4 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidineusing 2.4 mmol of (1S,2S)-1-butyl-2-(hydroxymethyl)oxirane is carriedout analogously to the procedure indicated for Example 7. Correspondingpurification gives 0.49 g (39%) of colorless crystals, X 84.5 S_(C) *166 S_(A) 174 I.

Example 9 Synthesis of2,3-difluoro-4-[5-(6-octyloxypyridin-3-yl)pyrimidin-2-yl]phenylheptanoate ##STR18##

2.7 mmol of DCC are introduced at room temperature into 50 ml ofdichloromethane, and 2.4 mmol of2-(2,3-difluoro-4-hydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine,2.7 mmol of heptanoic acid and 0.24 mmol of DMAP are added. The reactionmixture is left to stand overnight with exclusion of light, precipitateddicyclohexylurea is then filtered off, and the solvent is removed invacuo. The crude product is chromatographed on silica gel 60 usingdichloromethane/ethyl acetate 20:1 (v/v) as eluent and is recrystallizedfrom acetonitrile, giving 1.0 g (84%) of colorless crystals, X 88 S_(C)165 S_(A) 167.5 I.

Example 10 Synthesis of2,3-difluoro-4-[5-(8-octyloxpyridin-3-yl)pyrimidin-2-yl]phenyl ethylcarbonate ##STR19##

2.4 mmol of2-(2,3-difluorohydroxyphenyl)-5-(6-octyloxypyridin-3-yl)pyrimidine areintroduced into 20 ml of THF and cooled to 0° C. Firstly 2.7 mmol oftriethylamine and then 2.7 mmol of ethyl chlorocarbonate in 20 ml of THFare added dropwise, and the mixture is stirred at 0° C. for 1 hour. Thereaction mixture is left to stand overnight at room temperature andfiltered, the solvent is removed in vacuo, and the crude product ischromatographed on silica gel 60 using dichloromethane/ethyl acetate20:1 (v/v) as eluent. Recrystallization from acetonitrile gives 0.75 g(64%) of colorless crystals, X 74 S_(C) 92 S_(A) 165 N 172.5 I.

Example 11 Synthesis of5-(2,3-difluoro-4-octylphenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidine##STR20##

The reaction of 2 mmol of 5-bromo2-(6-hexyloxypyridin-3-yl)pyrimidine,2.2 mmol of 2,3-difluoro-4-octylphenylboronic acid, 4 mmol of sodiumcarbonate and 0.02 mmol of tetrakis(triphenylphosphine)palladium(0) in14 ml of toluene, 7 ml of ethanol and 7 ml of water is carried outAnalogously to the procedure indicated for Example 1a). The crudeproduct is separated off by column chromatography on silica gel 60 usingn-heptane/ethyl acetate 9:1 (v/v) as eluent and is recrystallized fromacetonitrile, giving 0.77 g (80%) of colorless crystals, X 104 S_(C) 94S_(A) 129 I.

Example 12 Synthesis of5-(4-decyl-2,3-difluorophenyl)-2-(6-hexyloxypyridin-3-yl)pyrimidine##STR21##

The reaction of 2 mmol of 5-bromo-2-(6-hexyloxypyridin-3-yl)pyrimidine,2 mmol of 4-decyl-2,3-difluorophenylboronic acid, 4 mmol of sodiumcarbonate and 0.02 mmol of tetrakis(triphenylphosphine)palladium(0) in 8ml of toluene, 3 ml of ethanol and 3 ml of water is carried outanalogously to the procedure indicated for Example 1a). The crudeproduct is separated off by column chromatography on silica gel 60 usingethyl acetate as eluent and is recrystallized from acetonitrile, giving0.4 g (39%) of colorless crystals, X 96 S_(A) 127 I.

Example 13 Synthesis of2-(6-butoxypyridin-3-yl)-5-(2,3-difluoro-4-octylphenyl)pyrimidine##STR22##

The reaction of 1.6 mmol of 5-bromo-2-(6-butoxypyridin-3-yl)pyrimidine,1.8 mmol of 2,3-difluoro-4-octylphenylboronic acid. 3.2 mmol of sodiumcarbonate and 0.02 mmol of tetrakis(triphenylphosphine)palladium(0) in10 ml of toluene, 5 ml of ethanol and 5 ml of water is carried outanalogously to the procedure indicated for Example 1a). The crudeproduct is separated off by column chromatography on silica get 60 usingheptane/ethyl acetate 9:1 (v/v) as eluent and is recrystallized fromacetonitrile, giving 0.53 g (73%) of colorless crystals, X 113 S_(A)132.5 I.

Example 14 Synthesis of5-(2,3-difluoro-4-octylphenyl)-2-(6-octyloxypyridin-3-yl)pyrimidine##STR23##

The reaction of 3.5 mmol of5-bromo-2-(6-octyloxypyridin-3-yl)pyrimidine, 3.85 mmol of2,3-difluoro-4-octylphenylboronic acid, 7 mmol of sodium carbonate and0.04 mmol of tetrakis(triphenylphosphine)palladium(0) in 20 ml oftoluene: 10 ml of ethanol and 10 ml of water it carried out analogouslyto the procedure indicated for Example 1a). The crude product isseparated off by column chromatography on silica gel 60 usingheptane/ethyl acetate 9:1 (v/v) as eluent and is recrystallized fromacetonitrile, giving 1.5 g (83%) of colorless crystals, X 105 S_(C) 104S_(A) 127 I.

Example 15 Synthesis of5-(2,3-difluorophenyl2-(6-hexyloxypyridin-3-yl)pyrimidine ##STR24##

The reaction of 2-chloro-5-(2,3-difluorophenyl)pyrimidine with2-hexyloxypyridine-5-boronic acid is carried out analogously to theprocedure indicated for Example 1a). Chromatographic purification onsilica gel 60 using dichloromethane/ethyl acetate 95:5 (v/v) as eluentand recrystallization from acetonitrile gives colorless crystals, m.p.110.5° C.

Example 16 Synthesis of2-(2,3-difluoro-4-octylphenyl)-5-(6-hexyloxypyridin-3-yl)pyrimidine##STR25##

The reaction of 2.5 mmol of2-chloro-5-(6-hexyloxypyridin-3-yl)pyrimidine, 2.5 mmol of2,3-difluoro-4-octylphenylboronic acid, 5 mmol of sodium carbonate and0.025 mmol of tetrakis(triphenylphosphine)palladium(0) in 8 ml oftoluene, 4 ml of ethanol and 4 ml of water is carried out analogously tothe procedure indicated for Example 1a). The crude product is separatedoff by column chromatography on silica gel 60 usingdichloromethane/ethyl acetate 98:2 (v/v) as eluent and is recrystallizedfrom acetonitrile, giving 0.47 g (39%) of colorless crystals, X 94.5S_(C) 125.5 S_(A) 156 I.

Example 17 Synthesis of5-(6-butoxypyridin-3-yl)-2-(2,3-difluoro-4-octylphenyl)pyrimidine##STR26##

The reaction of 2 mmol of 5-(6-butoxypyridin-3-yl)-2-chloropyrimidine,2.2 mmol of 2,3-difluoro-4-octylphenylboronic acid, 4 mmol of sodiumcarbonate and 0.02 mmol of tetrakis(triphenylphosphine)palladium(0) in10 ml of toluene, 5 ml of ethanol and 5 ml of water is carried outanalogously to the procedure indicated for Example 1a). The crudeproduct is separated off by column chromatography on silica gel 60 usingheptane/ethyl acetate 9:1 (v/v) as eluent and is recrystallized fromacetonitrile, giving 0.42 g (46%) of colorless crystals, X 84 S_(C) 73S_(A) 162 I.

Use examples

A basic mixture A comprises the following components:

    ______________________________________                                                                 % by wt.                                             ______________________________________                                         ##STR27##                 15.44                                               ##STR28##                 19.42                                               ##STR29##                 20.10                                               ##STR30##                 12.61                                               ##STR31##                 6.50                                                ##STR32##                 13.11                                               ##STR33##                 12.82                                              ______________________________________                                    

An FLC mixture B comprises the following components:

    ______________________________________                                                                   %                                                                             by wt.                                             ______________________________________                                        Basic mixture A              78                                                ##STR34##                   10                                                ##STR35##                   10                                                ##STR36##                    2                                               ______________________________________                                    

Use Example 1

An FLC mixture C comprises the following components:

    ______________________________________                                                                   %                                                                             by wt.                                             ______________________________________                                        Basic mixture A              68                                                ##STR37##                   10                                                ##STR38##                   10                                                ##STR39##                    2                                                ##STR40##                   10                                               ______________________________________                                    

Use Example 2

An FLC mixture D comprises the following components:

    ______________________________________                                                                   %                                                                             by wt.                                             ______________________________________                                        Basic mixture A              68                                                ##STR41##                   10                                                ##STR42##                   10                                                ##STR43##                    2                                                ##STR44##                   10                                               ______________________________________                                    

An FLC mixture E comprises the following components:

    ______________________________________                                                                     %                                                                             by                                                                            wt.                                              ______________________________________                                        Basic mixture A                68                                              ##STR45##                     10                                              ##STR46##                     10                                              ##STR47##                     10                                              ##STR48##                      2                                             ______________________________________                                    

Use Example 3

An FLC mixture F comprises the following components:

    ______________________________________                                                                     %                                                                             by                                                                            wt.                                              ______________________________________                                        Basic mixture A                58                                              ##STR49##                     10                                              ##STR50##                     10                                              ##STR51##                     10                                              ##STR52##                      2                                              ##STR53##                     10                                             ______________________________________                                    

Table: Phases and electro-optical properties

    __________________________________________________________________________                   V.sub.min                                                                        τ.sub.min                                                                    V.sub.min                                                                        τ.sub.min                                                                    V.sub.min                                                                        τ.sub.min                                                                    2e 2e                                        Mixture:                                                                            Ta/c                                                                             Ta/n                                                                             Tn/i                                                                             (Mo)                                                                             (Mo)                                                                             (M3)                                                                             (M3)                                                                             (JA)                                                                             (JA)                                                                             (5v)                                                                             (10v)                                     __________________________________________________________________________    B     62 75 82 65 18 55 63 60 18 16 23                                        C     61 77 86 53 20 46 7.6                                                                              53 20 20 28                                        (Use Ex.1)                                                                    D     66 78 83 55 24 51 9.1                                                                              58 26 18 27                                        (Use Ex.2)                                                                    E              60 17 51 6.8                                                                              60 17 15 28                                        F              40 22 40 6.5                                                                              42 27 19 30                                        (Use Ex.3)                                                                    __________________________________________________________________________

In the table, the symbols have the following meanings:

Ta/c: Phase transition temperature S_(C) →S_(A) [° C.]

Ta/n: Phase transition temperature S_(A) →S_(N) [° C.]

Tn/l: Phase transition temperature N→isotropic [° C.]

V_(min), τ_(min) : Minimum of the V,τ curve

Mo: Monopolar scheme

M3: Malvern 3 scheme (J. R. Hughes, E. P. Raynes, Liq. Cryst. 1993, 13,597; errata corrige, 1993, 15, 281).

JA: Joers-Alvey scheme (J. C. Jones, M. J. Towler, J. R Hughes, Display1993, 14, 86)

2e: Switching angle [°]

Mixtures containing a compound according to the invention have aconsiderably lower value for the use voltage at the minimum of the V,τcurve.

It is claimed:
 1. A difluorophenylpyrimidylpyridine derivative of theformula (I) ##STR54## in which the symbols are defined as follows: X isN and Y is CH or X is CH and Y is N;R¹ and R² are identical or differentand area) an unbranched or branched alkyl chain having 1 to 20 carbonatoms, whereaa) one or more non-adjacent and non-terminal CH₂ groups maybe replaced by --O--, --CO--O--, --O--CO--, --O--CO--O-- or --Si(CH₃)₂--, and/or ab) one or more H atoms may be replaced by F, and/or ac) theterminal CH₃ group may be replaced by one of the following chiral groups(optically active or racemic): ##STR55## b) hydrogen, where only one ofthe two radicals R¹ and R² can be H,with the proviso that R¹ must not bebonded to the pyridine ring via --CO--O-- or --O--CO--O--; R³, R⁴ and R⁵are identical or different and are hydrogen or a straight-chain orbranched alkyl radical having 1-16 carbon atoms (with or without anasymmetrical carbon atom), where, in addition, one or more non-adjacent,non-terminal CH₂ groups may be replaced by --O--, and/or where one ormore H atoms of the alkyl radical may be substituted by --F; R⁴ and R⁵may alternatively together be --(CH₂)₄ -- or --(CH₂)₅ -- if they arebonded to a dioxolane system.
 2. A difluorophenylpyrimidylpyridinederivative as claimed in claim 1, wherein the symbols in the formula (I)are defined as follows:R¹ and R² are identical or different and area) anunbranched or branched alkyl chain having 1 to 16 carbon atoms, whereaa)one or more non-adjacent and non-terminal CH₂ groups may be replaced by--O--, --CO--O--, O--CO--, --O--CO--O-- or --Si(CH₃)₂ --, and/or ab) oneor more H atoms may be replaced by F, and/or ac) the terminal CH₃ groupmay be replaced by one of the following chiral groups (optically activeor racemic): ##STR56## b) hydrogen, where only one of the two radicalsR¹ and R² can be H,with the proviso that R¹ must not be bonded to thepyridine ring via --CO--C-- or --O--CO--O--; R³, R⁴ and R⁵ are identicalor different and are hydrogen or a straight-chain or branched alkylradical having 1-13 carbon atoms, where, in addition, one or morenon-adjacent, non-terminal CH₂ groups may be replaced by --O--, and/orwhere one or more H atoms of the alkyl radical may be substituted by--F; R⁴ and R⁵ may alternatively together be --(CH₂)₄ -- or --(CH₂)₅ --if they are bonded to a dioxolane system.
 3. Adifluorophenylpyrimidylpyridine derivative as claimed in claim 2,wherein the symbols in the formula (I) are defined as follows:R¹ and R²are identical or different and area) an unbranched or branched alkylchain having 1 to 12 carbon atoms, whereaa) one or more non-adjacent andnon-terminal CH₂ groups may be replaced by --O--, --CO--O--, --O--CO--or --O--CO--O--, and/or ab) one or more H atoms may be replaced by F,and/or ac) the terminal CH₃ group may be replaced by one of thefollowing chiral groups (optically active or racemic): ##STR57## b)hydrogen, where only one of the two radicals R¹ and R² can be H,with theproviso that R¹ must not be bonded to the pyridine ring via --CO--O-- or--O--CO--O--; R³ is identical or different and is hydrogen or astraight-chain or branched alkyl radical having 1 to 10 carbon atoms,where, in addition, one or two non-adjacent, non-terminal CH₂ groups maybe replaced by --O--.
 4. A difluorophenylpyrimidylpyridine derivative asclaimed in claim 1, wherein the symbols in the formula (I) are definedas follows:R¹ and R² are identical or different and area) an unbranchedor branched alkyl chain having 1 to 12 carbon atoms, whereaa) one ormore non-adjacent and non-terminal CH₂ groups may be replaced by --O--,--CO--O--, --O--CO-- or --O--CO--C--, and/or ab) the terminal CH₃ groupmay be replaced by one of the following chiral groups (optically activeor racemic): ##STR58## b) hydrogen, where only one of the two radicalsR¹ and R² can be H,with the proviso that R¹ must not be bonded to thepyridine ring via --CO--O-- or --O--CO--O--; R³ is identical ordifferent and is hydrogen or a straight-chain or branched alkyl radicalhaving 1 to 10 carbon atoms, where, in addition, one or twonon-adjacent, non-terminal CH₂ groups may be replaced by --O--.
 5. Themethod of use of a difluorophenylpyrimidylpyridine derivative as claimedin claim 1 as a component of liquid-crystalline mixtures.
 6. Aliquid-crystal mixture comprising one or moredifluorophenylpyrimidylpyridine derivatives as claimed in claim
 1. 7. Aliquid-crystal mixture as claimed in claim 6, which is ferroelectric. 8.A liquid-crystal mixture as claimed in claim 6, which comprises from0.01 to 80% by weight of one or more difluorophenylpyrimidylpyridinederivatives of the formula (I).
 9. A ferroelectric switching and/ordisplay device containing a ferroelectric liquid-crystal mixture asclaimed in claim
 7. 10. A ferroelectric switching and/or display deviceas claimed in claim 9, which is operated in τV_(min) mode.